Evidence of child abuse, including child pornography, is often readily available via the Web thanks to peer-to-peer (P2P) file-sharing sites. BitTorrent software poses a particular problem for stopping the trade of these illicit images because it breaks the files into pieces and sends them from one computer to the next via different paths without passing through any centralized servers. This has for the most part rendered cops and security experts powerless to trace the origins of the files and catch the predators.

Recently, however, engineers at Oak Ridge National Laboratory in Tennessee have developed promising new software to automate the tracking of BitTorrent content and hopefully help law-enforcement officials solve this puzzle. The key is locating the images quickly by focusing on new files coming out of RSS feeds and entering P2P networks, before they can be widely distributed.

The more times a file has been downloaded via a P2P network the more widely distributed the contents of that file are, making it much more difficult to track, says Robert Patton, an applied software engineering researcher at Oak Ridge who is developing the software with Thomas Potok, head of the lab's Applied Software Engineering Research Group.

Child predators can share images, videos or other content by first creating a small descriptor file, or "torrent," that can be distributed via the Web or e-mail. The torrent file will tell anyone interested in downloading this content how to contact a "tracker" computer that coordinates the matching of consumers with suppliers. Because of the way BitTorrent works, the consumer ends up getting different pieces of content from multiple computers with different IP (Internet Protocol) addresses.

Oak Ridge's software grabs the torrent file and immediately investigates the IP addresses of the different computers from which pieces of the file are stored. Based on data-traffic patterns, the software then prioritizes IP addresses to be investigated, creating a short list of suspects for cops to investigate.

The federal government estimates that more than five children die every day as a result of child abuse. As it is, law enforcement has the resources to work on less then 1 percent of the caseload, says Grier Weeks, executive director of the National Association to Protect Children, a nonprofit based in Knoxville, Tenn. Oak Ridge's automated winnowing of suspects is expected to be a valuable time-saver for law enforcement hunting down those computers and their owners. Currently cops have too many IP addresses, most of them dead ends, to investigate.

Oak Ridge's work on the BitTorrent tool began in early 2010 when the association asked researchers at Oak Ridge and law enforcement officials from Tennessee and Virginia to educate them on the pervasiveness of child abuse and exploitation, much of it shared on the Internet. The idea was for the association to connect Oak Ridge's scientists with law enforcement overwhelmed by the magnitude of the problem and hindered by technical challenges. The Knoxville Police Department, home of the Tennessee Internet Crimes against Children Task Force, expressed interest in Oak Ridge's work soon after meeting the researchers.

Oak Ridge's software means that sophisticated methods of data analysis may soon be in the hands of law enforcement officials. Two police departments are now testing it, although Weeks declined to identify them. "This is a Geiger counter for locating predatory pedophiles," he says. "Instead of radiation, it finds the presence of child abuse images."

The biggest concern about the software at this point is whether its use will hold up in court or allow potential offenders to get off on some technicality. If the software does prove successful, however, "there will be one less excuse for inaction, which is what we have now," says Weeks, who adds that he has brought the software to the attention of top law enforcement agencies, including the U.S. Department of Homeland Security. "This is an entirely new field really, what we would call child-rescue technology, and it uses the same sorts of tools and methods as are used in counterterrorism."

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